430的RTC问题

以MSP430F6733为例RTC_C会有提供一个a keep-out window，在这段时间里面更新是安全的。

24.2.5 Reading or Writing Real-Time Clock Registers
Because the system clock may in fact be asynchronous to the RTC_C clock source, special care must be
used when accessing the real-time clock registers.
SLAU208M–June 2008–Revised February 2013 Real-Time Clock C (RTC_C) 625
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The real-time clock registers are updated once per second. To prevent reading any real-time clock register
at the time of an update that could result in an invalid time being read, a keep-out window is provided. The
keep-out window is centered approximately 128/32768 seconds around the update transition. The read
only RTCRDY bit is reset during the keep-out window period and set outside the keep-out the window
period. Any read of the clock registers while RTCRDY is reset is considered to be potentially invalid, and
the time read should be ignored.
An easy way to safely read the real-time clock registers is to utilize the RTCRDYIFG interrupt flag. Setting
RTCRDYIE enables the RTCRDYIFG interrupt. Once enabled, an interrupt is generated based on the
rising edge of the RTCRDY bit, causing the RTCRDYIFG to be set. At this point, the application has
nearly a complete second to safely read any or all of the real-time clock registers. This synchronization
process prevents reading the time value during transition. The RTCRDYIFG flag is reset automatically
when the interrupt is serviced or can be reset with software.